The newly outlined US strategy to fight the Islamic State (IS) hinges on cooperation with Middle East allies and rebels on the ground, but it remains unclear just how reliable they are.

On September 18, the Senate backed US President Barack Obama's plan to arm moderate rebels in Syria, in a bid to defeat the IS.

Washington frets that the IS could carve out a safe haven in the Middle East from which they can strike the US homeland, just as Al Qaeda did in Afghanistan in the lead-up to the September 11 attacks.

The IS has in recent months overrun vast swaths of northern Iraq and vowed to take Baghdad in an effort to establish an official state governed by radical Islamist theology.

Despite ongoing US air bombardments of IS positions in Iraq and now Syria, some experts say boots on the ground are also needed to defeat the radicals.

But the US plan to partner with moderate rebels on the ground raises myriad questions: Are moderate rebels reliable? And if so, do they have the military capability to take on a battle with a hardened, well-financed and extremely motivated foe?

It also remains unknown how the president plans to keep US weapons out of the wrong hands and get them into the hands of moderate rebels, Steve Scalise, a House Republican, told Fox News on Friday. And Obama's strategy to vet potential US partners on the ground in Syria is also unclear.

Arab states with which Washington is allied present another list of unknowns, as many appear to be doing the minimum to help the US battle IS, some experts said.

Indeed, Arab allies fear retaliation by the IS and its sympathizers within their own populations, said Wayne White, former deputy director of the State Department's Middle East Intelligence Office.

Among some Arab allies, there is a concern that serious blows against the IS in Syria, such as the strikes launched this week, might benefit the government of Bashar al-Assad, a government that so many regional leaders have long wanted to see taken down, White told Xinhua.

As for Egypt, the government is distracted by its own internal security problems, especially in or emanating from the Sinai, the continuing deterioration of the situation in adjacent Libya, and the need to bolster security along the Egyptian-Libyan frontier, he said.

Turkey, particularly in its refusal of the use of its air bases by the US, has been a major disappointment.

And the other critical bordering state, Jordan, has waved off just about everything except intelligence cooperation, White noted.

The author is a correspondent for the Xinhua News Agency. opinion@globaltimes.com.cn